Liquid crystal display

ABSTRACT

An LCD includes a first TAC film, a first optical uniaxial phase compensating film, an LC cell, a second optical uniaxial phase compensating film and a second TAC film from the incident surface to the emitting surface. The first optical uniaxial phase compensating film is used for providing a first compensating value and a second compensating value by adjusting thickness and by adjusting a first refractive index, a second refractive index, and a third refractive index. The second optical uniaxial phase compensating film is used for providing a third compensating value by adjusting thickness and by adjusting a fourth refractive index, a fifth refractive index, and a sixth refractive index. Leakage of light is controlled according to the first compensating value, the second compensating value, and the third compensating value in the LCD.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD), andmore particularly, to an LCD comprising an optical uniaxial phasecompensating film.

2. Description of the Prior Art

Owing to their low-profile, thin, and lightweight features, LCDs havebecome the mainstream display devices in recent years. Liquid crystalscreens are widely used in electronic devices such as cellphones,personal digital assistants (PDAs), digital cameras, computers,notebooks, etc.

An LCD comprises an LC cell. An alignment of LC molecules in the LC cellis determined by variation of an electric field applied on the LC cell,and the transmission of light in the LC cell is adjusted accordingly. AnLC material has a property of birefringence, which means that therefractive index of light in the direction of the long axis of themolecules is different from the refractive index of light in thedirection of the short axis of the molecules. Therefore, linearlypolarized incident light has diverse phases through different paths inthe LC cell in the polarized direction. The feature of color and thetransmission of light at a slant viewing angle are different from thoseat a front viewing angle.

Birefringence index of the LC molecules in the LC cell varies with anobservation inclination. With the observation inclination increases,both of the contrast ratio of an image and image resolution decrease. Toenhance the contrast ratio of the image obviously at a specific viewingangle and to reduce leakage of light in dark state on the LCD, acompensating film is attached to the LC panel of a conventional LCD. Thebirefringence of the LC molecules can be symmetrically compensatedbecause the retardation value of light in different directions iscompensated using the compensating film.

Please refer to FIG. 1 and FIG. 2, FIG. 1 shows a simulation of adistribution of light leakage in dark state after being compensated by aconventional uniaxial retardation film. FIG. 2 shows a simulation of adistribution of contrast over all viewing angles after being compensatedby the conventional uniaxial retardation film. The optical pathdifference of liquid crystal Δn×d is set at 315 nm. The retardationvalues Ro and Rth of the A plate retardation film are 58 nm and 220 nm,respectively, and the retardation value Rth of the C plate is 40 nm. Ascan be seen from FIG. 1 and FIG. 2, under these circumstances there issevere light leakage problem in a horizontal viewing area. Generally,since the horizontal viewing area at is more visible than a verticalviewing area, contrast ratio and clarity in the horizontal viewing areaaffects viewing quality for observers than the vertical viewing area.

As a result, it is necessary to restrict the area of leakage of light indark state within the vertical viewing area, rather than the horizontalviewing area.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an LCD adopting anoptical uniaxial phase compensating film. The compensating value of theoptical uniaxial phase compensating film can be adjusted by adjustingthickness of the optical uniaxial phase compensating film or therefractive index of the optical uniaxial phase compensating film. Theadvantage of the LCD adopting the optical uniaxial phase compensatingfilm is that the area of leakage of light in dark state is restricted tothe vertical viewing area.

According to the present invention, a liquid crystal display (LCD)comprises a backlight source for generating light; a first triacetatecellulose (TAC) film; a first polyvinyl alcohol (PVA) film; a firstoptical uniaxial phase compensating film, for providing a firstcompensating value and a second compensating value by adjustingthickness of the first optical uniaxial phase compensating film and byadjusting a first refractive index, a second refractive index, and athird refractive index corresponding to light in a first direction, thelight in a second direction, and the light in a third direction,respectively; a liquid crystal (LC) cell; a second optical uniaxialphase compensating film, for providing a third compensating value byadjusting thickness of the second optical uniaxial phase compensatingfilm and by adjusting a fourth refractive index, a fifth refractiveindex, and a sixth refractive index corresponding to the light in thefirst direction, the light in the second direction, and the light in thethird direction, respectively; a second PVA film; and a second TAC film.Light leakage in dark state at a wide viewing angle being controlledaccording to the first compensating value, the second compensatingvalue, and the third compensating value in the LCD. The firstcompensating value is determined by an equation as follows:Ro_(A)=(Nx_(A)−Ny_(A))×D_(A) where RthA indicates the first compensatingvalue, NxA and NyA indicate refractive indexes corresponding to the X-and Y-axes of three-dimensional Cartesian coordinates for the firstoptical uniaxial phase compensating film, respectively, and DA indicatesthickness of the first optical uniaxial phase compensating film. Anoptical path difference of the LC cell is determined by (ne−no)×d, theoptical path difference is between 305.8 nm and 324.2 nm, where ne andno indicate an extraordinary refractive index and an ordinary refractiveindex of the LC cell, respectively, d indicates thickness of the LCcell, the first compensating value of the first optical uniaxial phasecompensating film is between 55 nm and 78 nm, and the secondcompensating value of the first optical uniaxial phase compensating filmis between 208 nm and 293 nm, the third compensating value of the secondoptical uniaxial phase compensating film is between the Y₁ nm and Y₂ nmwhere Y₁=0.004174x2−3.119x+555.5 and Y₂=−0.005882x2+1.733x+25.9 stand,and x indicates the second compensating value.

In one aspect of the present invention, the second compensating value isdetermined by an equation as follows:Rth_(A)=[(Nx_(A)+Ny_(A))/2−Nz_(A)]×D_(A) where Rth_(A) indicates thesecond compensating value, NxA, NyA, and NzA indicate refractive indexescorresponding to the X-, Y-, and Z-axes of three-dimensional Cartesiancoordinates for the first optical uniaxial phase compensating film,respectively, and DA indicates thickness of the first optical uniaxialphase compensating film.

In another aspect of the present invention, a pretilt angle of LCmolecules in the LC cell is 89 degrees.

In another aspect of the present invention, the third compensating valueis determined by the fourth refractive index, the fifth refractiveindex, the sixth refractive index, and thickness of the second opticaluniaxial phase compensating film.

In another aspect of the present invention, the first optical uniaxialphase compensating film is an A-plate compensating film, an optical axisof the first optical uniaxial phase compensating film and a surface ofthe first optical uniaxial phase compensating film are in parallel, thesecond optical uniaxial phase compensating film is a C-platecompensating film, and an optical axis of the second optical uniaxialphase compensating film is vertical to a surface of the second opticaluniaxial phase compensating film.

In still another aspect of the present invention, the LCD furthercomprises a first pressure sensitive adhesive (PSA). The first PSA isdisposed between the first optical uniaxial phase compensating film andthe LC cell.

In yet another aspect of the present invention, the LCD furthercomprises a second PSA. The second PSA is disposed between the secondoptical uniaxial phase compensating film and the LC cell.

According to the present invention, a liquid crystal display (LCD)comprises a backlight source for generating light; a first triacetatecellulose (TAC) film; a first polyvinyl alcohol (PVA) film; a firstoptical uniaxial phase compensating film, for providing a firstcompensating value and a second compensating value by adjustingthickness of the first optical uniaxial phase compensating film and byadjusting a first refractive index, a second refractive index, and athird refractive index corresponding to light in a first direction, thelight in a second direction, and the light in a third direction,respectively; a liquid crystal (LC) cell; a second optical uniaxialphase compensating film, for providing a third compensating value byadjusting thickness of the second optical uniaxial phase compensatingfilm and by adjusting a fourth refractive index, a fifth refractiveindex, and a sixth refractive index corresponding to the light in thefirst direction, the light in the second direction, and the light in thethird direction, respectively; a second PVA film; and a second TAC film.Light leakage in dark state at a wide viewing angle is controlledaccording to the first compensating value, the second compensatingvalue, and the third compensating value in the LCD. The firstcompensating value is determined by an equation as follows:Ro_(A)=(Nx_(A)−Ny_(A))×D_(A) where RthA indicates the first compensatingvalue, NxA and NyA indicate refractive indexes corresponding to the X-and Y-axes of three-dimensional Cartesian coordinates for the firstoptical uniaxial phase compensating film, respectively, and DA indicatesthickness of the first optical uniaxial phase compensating film. Thefirst compensating value of the first optical uniaxial phasecompensating film is between 55 nm and 78 nm

In another aspect of the present invention, an optical path differenceof the LC cell is determined by (ne−no)×d, the optical path differenceis between 305.8 nm and 324.2 nm, where ne and no indicate anextraordinary refractive index and an ordinary refractive index of theLC cell, respectively, d indicates thickness of the LC cell.

In another aspect of the present invention, the second compensatingvalue is determined by an equation as follows:Rth_(A)=[(Nx_(A)+Ny_(A))/2−Nz_(A)]×D_(A) where RthA indicates the secondcompensating value, NxA, NyA, and NzA indicate refractive indexescorresponding to the X-, Y-, and Z-axes of three-dimensional Cartesiancoordinates for the first optical uniaxial phase compensating film,respectively, and DA indicates thickness of the first optical uniaxialphase compensating film.

In another aspect of the present invention, the second compensatingvalue of the first optical uniaxial phase compensating film is between208 nm and 293 nm.

In another aspect of the present invention, a pretilt angle of LCmolecules in the LC cell is 89 degrees.

In another aspect of the present invention, the third compensating valueis determined by the fourth refractive index, the fifth refractiveindex, the sixth refractive index, and thickness of the second opticaluniaxial phase compensating film.

In another aspect of the present invention, the third compensating valueof the second optical uniaxial phase compensating film is between the Y₁nm and Y₂ nm where Y₁=0.004174x2−3.119x+555.5 andY₂=−0.005882x2+1.733x+25.9 stand, and x indicates the secondcompensating value.

In another aspect of the present invention, the first optical uniaxialphase compensating film is an A-plate compensating film, an optical axisof the first optical uniaxial phase compensating film and a surface ofthe first optical uniaxial phase compensating film are in parallel. Thesecond optical uniaxial phase compensating film is a C-platecompensating film, and an optical axis of the second optical uniaxialphase compensating film is vertical to a surface of the second opticaluniaxial phase compensating film.

In still another aspect of the present invention, the LCD furthercomprises a first pressure sensitive adhesive (PSA). The first PSA isdisposed between the first optical uniaxial phase compensating film andthe LC cell.

In yet another aspect of the present invention, the LCD furthercomprises a second PSA. The second PSA is disposed between the secondoptical uniaxial phase compensating film and the LC cell.

Compared with prior art, the present invention comprises an LCDcomprising an optical uniaxial phase compensating film. When opticalpath difference of the LC cell is between 305.8 nm and 324.2 nm (theoptical path difference which the wavelength of 550 nm corresponds to)and that the pretilt angle of LC molecules is 89 degrees, the firstcompensating value Ro_(A) of the first optical uniaxial phasecompensating film needs to be between 55 nm and 78 nm and the secondcompensating value Rth_(A) of the first optical uniaxial phasecompensating film 123 needs to be between 208 nm and 293 nm. Besides,the third compensating value Rth_(C) of the second optical uniaxialphase compensating film needs to be between the Y₁ nm and Y₂ nm whereY₁=0.004174x2−3.119x+555.5 and Y₂=−0.005882x2+1.733x+25.9 stand, and xindicates the second compensating value Rth_(A). The present inventionproperly adopts the first compensating value Ro_(A) of the first opticaluniaxial phase compensating film, the second compensating value Rth_(A)of the first optical uniaxial phase compensating film, and the thirdcompensating value Rth_(C) of the second optical uniaxial phasecompensating film. Serious light leakage in dark state in the area atthe horizontal viewing angle in the conventional optical uniaxial phasecompensating film is effectively improved if the present invention isadopted. Besides, both of the contrast ratio and the clarity in the areaat the horizontal viewing angle are improved as well.

These and other features, aspects and advantages of the presentdisclosure will become understood with reference to the followingdescription, appended claims and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simulation of a distribution of light leakage in darkstate after being compensated by a conventional uniaxial retardationfilm.

FIG. 2 shows a simulation of a distribution of contrast over all viewingangles after being compensated by the conventional uniaxial retardationfilm.

FIG. 3 shows a schematic diagram of an LCD according to a preferredembodiment of the present invention.

FIGS. 4 to 6 respectively show relationship diagrams between leakagevalues and different first compensating values Ro_(A) of the firstoptical uniaxial phase compensating film, different second compensatingvalues Rth_(A) of the first optical uniaxial phase compensating film,and different third compensating values Rth_(C) of the second opticaluniaxial phase compensating film on condition that the optical pathdifference of the LC cell is 305.8 nm, 315 nm, and 324.2 nm.

FIG. 7 shows a simulation of a distribution of light leakage in darkstate upon conditions that optical path difference of the LC cell of305.8 nm, the first optical uniaxial phase compensating film with thefirst compensating value Ro_(A) of 71 nm and the second compensatingvalue Rth_(A) of 269 nm and by the second optical uniaxial phasecompensating film with the third compensating value Rth_(A) of 24 nm.

FIG. 8 shows a simulation of a distribution of contrast over all viewingangles based on the conditions illustrated in FIG. 7.

FIG. 9 shows a simulation of a distribution of light leakage in darkstate upon conditions that optical path difference of the LC cell of 315nm, the first optical uniaxial phase compensating film with the firstcompensating value Ro_(A) of 65 nm and the second compensating valueRth_(A) of 244 nm and by the second optical uniaxial phase compensatingfilm with the third compensating value Rth_(A) of 75 nm.

FIG. 10 shows a simulation of a distribution of contrast over allviewing angles based on the conditions illustrated in FIG. 9.

FIG. 11 shows a simulation of a distribution of light leakage in darkstate upon conditions that optical path difference of the LC cell of324.2 nm, the first optical uniaxial phase compensating film with thefirst compensating value Ro_(A) of 58 nm and the second compensatingvalue Rth_(A) of 220 nm and by the second optical uniaxial phasecompensating film with the third compensating value Rth_(A) of 95 nm.

FIG. 12 shows a simulation of a distribution of contrast over allviewing angles based on the conditions illustrated in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures.

Please refer to FIG. 3. FIG. 3 shows a schematic diagram of an LCD 10according to a preferred embodiment of the present invention. The LCD 10comprises a liquid crystal (LC) cell 16, a first polarizer 12, a secondpolarizer 14, and a backlight source 18. The backlight source 18 is usedfor generating light. The LC cell 16 is glued to an area between thefirst polarizer 12 and the second polarizer 14 with a pressure sensitiveadhesive (PSA) 2. The first polarizer 12 and the second polarizer 14 areused for deflecting an incident light. A first optical axis of the firstpolarizer 12 is perpendicular to a second optical axis of the secondpolarizer 14.

The first polarizer 12 comprises a first polyvinyl alcohol (PVA) film121, a first triacetate cellulose (TAC) film 122, and a first opticaluniaxial phase compensating film 123. The PVA film 121 is insertedbetween the first TAC film 122 and the first optical uniaxial phasecompensating film 123. The second polarizer 14 comprises a second PVAfilm 141, a second optical uniaxial phase compensating film 142, and athird TAC film 143. The second PVA film 141 is inserted between thesecond optical uniaxial phase compensating film 142 and the third TACfilm 143. In this embodiment, the first optical uniaxial phasecompensating film 123 is an A-plate compensating film. The optical axisof the first optical uniaxial phase compensating film 123 and thesurface of the first optical uniaxial phase compensating film 123 are inparallel. The second optical uniaxial phase compensating film 142 is aC-plate compensating film. The optical axis of the second opticaluniaxial phase compensating film 142 is vertical to the surface of thesecond optical uniaxial phase compensating film 142. The first opticaluniaxial phase compensating film 123 is used for providing a firstcompensating value Ro_(A) and a second compensating value Rth_(A). Thesecond optical uniaxial phase compensating film 142 is used forproviding a third compensating value Rth_(C). The slow axis of the firstoptical uniaxial phase compensating film 123 forms a 90 degree anglewith the absorption axis of the first PVA film 121. The slow axis of thesecond optical uniaxial phase compensating film 142 forms a zero degreeangle with the absorption axis of the second PVA film 141. The method ofdetermination of the first compensating value, the second compensatingvalue, and the third compensating value will be detailed in thefollowing description. The optical path difference of the LC cell 16,the compensating value of the first optical uniaxial phase compensatingfilm 123, and the compensating values of the second optical uniaxialphase compensating film 142 are values corresponding to a wavelength of550 nm in the following embodiment.

Please refer to FIGS. 4 to 6. FIGS. 4 to 6 respectively showrelationship diagrams between leakage values and different firstcompensating values Ro_(A) of the first optical uniaxial phasecompensating film 123, different second compensating values Rth_(A) ofthe first optical uniaxial phase compensating film 123, and differentthird compensating values Rth_(C) of the second optical uniaxial phasecompensating film 142 on condition that the optical path difference ofthe LC cell 16 is 305.8 nm, 315 nm, and 324.2 nm. For a simplerdescription, the incident light generated by the backlight source 18belongs to Lambertian distribution in this embodiment. Luminance in thecenter of the incident light is defined as 100 nit. The pretilt angle ofthe LC molecules in the LC cell 16 is 89 angles. The optical pathdifference of the LC cell 16 is determined by Δn×d. The optical pathdifference of the LC cell 16 is between 305.8 nm and 324.2 nm where neindicates an extraordinary refractive index of the LC cell 16, ne and noindicate an extraordinary refractive index and an ordinary refractiveindex of the LC cell 16, respectively, and d indicates thickness of theLC cell 16.

In FIGS. 4-6, Ro_(A) indicates the first compensating value of the firstoptical uniaxial phase compensating film 123 in the X-Y plane. Rth_(A)indicates the second compensating value of the first optical uniaxialphase compensating film 123 in the Z-axial direction. Rth_(C) indicatesthe third compensating value of the second optical uniaxial phasecompensating film 142 in the Z-axial direction. Ro_(A), Rth_(A), andRth_(C) are determined by values plugged into the following equations:Ro _(A)=(Nx _(A) −Ny _(A))×D _(A)  Equation 1,Rth _(A)=[(Nx _(A) +Ny _(A))/2−Nz _(A) ]×D _(A)  Equation 2,Rth _(C)=[(Nx _(C) +Ny _(C))/2−Nz _(C) ]×D _(C)  Equation 3,

where Nx_(A), Ny_(A), and Nz_(A) indicate refractive indexes of thelight generated by the backlight source 18 corresponding to the X-, Y-,and Z-axes of three-dimensional Cartesian coordinates, respectively,when the light passes through the first optical uniaxial phasecompensating film 123. Nx_(C), Ny_(C), and Nz_(C) indicate refractiveindexes of the light generated by the backlight source 18 correspondingto the X-, Y-, and Z-axes of three-dimensional Cartesian coordinates,respectively, when the light passes through the second phasecompensating film 142. D_(A) and D_(C) indicate thickness of the firstoptical uniaxial phase compensating film 123 and thickness of the secondphase compensating film 142, respectively.

FIGS. 4-6 show that in different LC optical path differences, thecompensating value of the first optical uniaxial phase compensating film123 and the compensating value of the second optical uniaxial phasecompensating film 142 have similar influential tendencies on the lightleakage in dark state. In other words, in different LC optical pathdifferences, the range of the compensating value is the same for theminimum light leakage in dark state.

As shown in FIGS. 4 to 6, different pretilt angles of LC molecules andthe different compensating values are simulated and the pretilt angle of89 degrees is calculated. In the range of 305.8 nm≦Δn×d≦324.2 nm and thelight leakage in dark state is smaller than 0.2 nit, the range ofcompensating value of the first optical uniaxial phase compensating film123 and the range of compensating value of the second optical uniaxialphase compensating film 142 are calculated. That is, on condition thatthe optical path difference of the LC cell is between 305.8 nm and 324.2nm and that the pretilt angle of LC molecules is 89 degrees, the LCD 10can still refrain light from leaking based on the first compensatingvalue Ro_(A) of the first optical uniaxial phase compensating film 123,the second compensating value Rth_(A) of the first optical uniaxialphase compensating film 123, and the third compensating value Rth_(C) ofthe second optical uniaxial phase compensating film 142. It is necessaryto control the first compensating value Ro_(A) of the first opticaluniaxial phase compensating film 123 to be between 55 nm and 78 nm andthe second compensating value Rth_(A) of the first optical uniaxialphase compensating film 123 to be between 208 nm and 293 nm. Further, itis necessary to adjust the third compensating value Rth_(C) of thesecond optical uniaxial phase compensating film 142 based on theadjusted the second compensating value Rth_(A) to control the thirdcompensating value Rth_(C) to be between the Y₁ nm and Y₂ nm whereY₁=0.004174x2−3.119x+555.5 and Y₂=−0.005882x2+1.733x+25.9, and xindicates the second compensating value Rth_(A).

Therefore, the first compensating value Ro_(A) of the first opticaluniaxial phase compensating film 123, the second compensating valueRth_(A) of the first optical uniaxial phase compensating film 123, andthe third compensating value Rth_(C) of the second optical uniaxialphase compensating film 142 are all for the incident light with thewavelength of 550 nm. When a compensating value is within theabove-mentioned range, the LCD will obtain the best compensation and theminimum light leakage in dark state.

Please refer to FIGS. 7 through FIG. 12, FIG. 7 shows a simulation of adistribution of light leakage in dark state upon conditions that opticalpath difference of the LC cell 16 of 305.8 nm, the first opticaluniaxial phase compensating film 123 with the first compensating valueRo_(A) of 71 nm and the second compensating value Rth_(A) of 269 nm andby the second optical uniaxial phase compensating film 142 with thethird compensating value Rth_(A) of 24 nm. FIG. 8 shows a simulation ofa distribution of contrast over all viewing angles based on theconditions illustrated in FIG. 7. FIG. 9 shows a simulation of adistribution of light leakage in dark state upon conditions that opticalpath difference of the LC cell 16 of 315 nm, the first optical uniaxialphase compensating film 123 with the first compensating value Ro_(A) of65 nm and the second compensating value Rth_(A) of 244 nm and by thesecond optical uniaxial phase compensating film 142 with the thirdcompensating value Rth_(A) of 75 nm. FIG. 10 shows a simulation of adistribution of contrast over all viewing angles based on the conditionsillustrated in FIG. 9. FIG. 11 shows a simulation of a distribution oflight leakage in dark state upon conditions that optical path differenceof the LC cell 16 of 324.2 nm, the first optical uniaxial phasecompensating film 123 with the first compensating value Ro_(A) of 58 nmand the second compensating value Rth_(A) of 220 nm and by the secondoptical uniaxial phase compensating film 142 with the third compensatingvalue Rth_(A) of 95 nm. FIG. 12 shows a simulation of a distribution ofcontrast over all viewing angles based on the conditions illustrated inFIG. 11.

When comparing FIGS. 7, 9, 11 with FIG. 1, it is observed that, afterbeing compensated by the first optical uniaxial phase compensating film123 and the second optical uniaxial phase compensating film 142according to the embodiment of the present invention, the light leakagein dark state is much less than that after being compensated by theprior art, and the light leakage area is restricted to a narrower areaat vertical viewing angle. When comparing FIGS. 8, 10, 12 with FIG. 2,it is observed that the contrast distribution over all viewing anglesafter being compensated by the compensation system according to theembodiment of the present invention is superior that after beingcompensated by the prior art, especially in the area at horizontalviewing angle.

The person skilled in the art can adjust the refractive index or thethickness of the first optical uniaxial phase compensating film 123 andthe refractive index or the thickness of the second optical uniaxialphase compensating film 142 using Equation 1, Equation 2, and Equation 3after obtaining the first compensating value Ro_(A) of the first opticaluniaxial phase compensating film 123, the second compensating valueRth_(A) of the first optical uniaxial phase compensating film 123, andthe third compensating value Rth_(C) of the second optical uniaxialphase compensating film 142.

Compared with the prior art, the present invention properly adopts thefirst compensating value Ro_(A) of the first optical uniaxial phasecompensating film 123, the second compensating value Rth_(A) of thefirst optical uniaxial phase compensating film 123, and the thirdcompensating value Rth_(C) of the second optical uniaxial phasecompensating film 142. Serious light leakage in dark state in the areaat the horizontal viewing angle in the conventional optical uniaxialphase compensating film is effectively improved if the present inventionis adopted. Besides, both of the contrast ratio and the clarity in thearea at the horizontal viewing angle are improved as well.

While the present invention has been described in connection with whatis considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements made withoutdeparting from the scope of the broadest interpretation of the appendedclaims.

What is claimed is:
 1. A liquid crystal display (LCD), comprising: abacklight source for generating light; a first triacetate cellulose(TAC) film; a first polyvinyl alcohol (PVA) film; a first opticaluniaxial phase compensating film, for providing a first compensatingvalue and a second compensating value by adjusting thickness of thefirst optical uniaxial phase compensating film and by adjusting a firstrefractive index, a second refractive index, and a third refractiveindex corresponding to light in a first direction, the light in a seconddirection, and the light in a third direction, respectively; a liquidcrystal (LC) cell; a second optical uniaxial phase compensating film,for providing a third compensating value by adjusting thickness of thesecond optical uniaxial phase compensating film and by adjusting afourth refractive index, a fifth refractive index, and a sixthrefractive index corresponding to the light in the first direction, thelight in the second direction, and the light in the third direction,respectively; a second PVA film; and a second TAC film; light leakage indark state at a wide viewing angle being controlled according to thefirst compensating value, the second compensating value, and the thirdcompensating value in the LCD; the first compensating value beingdetermined by an equation as follows: Ro_(A)=(Nx_(A)−Ny_(A))×D_(A) whereRo_(A) indicates the first compensating value, Nx_(A) and Ny_(A)indicate refractive indexes corresponding to the X- and Y-axes ofthree-dimensional Cartesian coordinates for the first optical uniaxialphase compensating film, respectively, and D_(A) indicates thickness ofthe first optical uniaxial phase compensating film, wherein an opticalpath difference of the LC cell is determined by (ne−no)×d, the opticalpath difference is between 305.8 nm and 324.2 nm, where ne and noindicate an extraordinary refractive index and an ordinary refractiveindex of the LC cell, respectively, d indicates thickness of the LCcell, the first compensating value of the first optical uniaxial phasecompensating film is between 55 nm and 78 nm, and the secondcompensating value of the first optical uniaxial phase compensating filmis between 208 nm and 293 nm, the third compensating value of the secondoptical uniaxial phase compensating film is between the Y₁ nm and Y₂ nmwhere Y₁=0.004174x2−3.119x+555.5 and Y₂=−0.005882x2+1.733x+25.9 stand,and x indicates the second compensating value.
 2. The LCD as claimed inclaim 1, wherein the second compensating value is determined by anequation as follows: Rth_(A)=[(Nx_(A)+Ny_(A))/2−Nz_(A)]×D_(A) whereRth_(A) indicates the second compensating value, Nx_(A), Ny_(A), andNz_(A) indicate refractive indexes corresponding to the X-, Y-, andZ-axes of three-dimensional Cartesian coordinates for the first opticaluniaxial phase compensating film, respectively, and D_(A) indicatesthickness of the first optical uniaxial phase compensating film.
 3. TheLCD as claimed in claim 1, wherein a pretilt angle of LC molecules inthe LC cell is 89 degrees.
 4. The LCD as claimed in claim 1, wherein thethird compensating value is determined by the fourth refractive index,the fifth refractive index, the sixth refractive index, and thickness ofthe second optical uniaxial phase compensating film.
 5. The LCD asclaimed in claim 1, wherein the first optical uniaxial phasecompensating film is an A-plate compensating film, an optical axis ofthe first optical uniaxial phase compensating film and a surface of thefirst optical uniaxial phase compensating film are in parallel, thesecond optical uniaxial phase compensating film is a C-platecompensating film, and an optical axis of the second optical uniaxialphase compensating film is vertical to a surface of the second opticaluniaxial phase compensating film.
 6. The LCD as claimed in claim 1further comprising a first pressure sensitive adhesive (PSA), whereinthe first PSA is disposed between the first optical uniaxial phasecompensating film and the LC cell.
 7. The LCD as claimed in claim 6further comprising a second PSA, wherein the second PSA is disposedbetween the second optical uniaxial phase compensating film and the LCcell.